The present invention relates to thin film magnetic tape recording heads for accessing magnetic tape possessing a high degree of alignment between read elements and write elements accessing a particular data track.
Reliability, cost-efficiency, and ease of use make magnetic tape the medium of choice for many information storage and retrieval applications. Typically, multiple data tracks are written simultaneously by write elements in a tape head. Similarly, multiple read elements are used to simultaneously sense multiple data tracks. The desire to increase information density held by magnetic tape has resulted in narrower and more closely spaced data tracks. This results in the need for close alignment between head elements which access each data track. This is particularly true for read-after-write operations in which data is read immediately following the write operation to verify the correctness of recorded data.
A tape head generally contains multiple write elements to simultaneously write multiple tracks for achieving a high rate of data transfer. Multiple read elements are used to achieve the same rate of data transfer during play back operations. The tape head is constructed using thin film techniques to permit the small element geometry required for high information density recording and to reduce the cost of production by applying replication and manufacturing techniques similar to those used in integrated circuit production. Many tape head designs are possible. One design consists of separate read modules and write modules. Each write module includes multiple write elements spaced across the tape surface. Similarly, each read module consists of multiple read elements spaced across the tape surface. The tape head is constructed by attaching read and write modules. A typical construction has one write module sandwiched between two read modules to permit read-after-write operation in either tape direction. Tape heads of this design are described in U.S. patent applications Ser. No. 08/939,773 titled xe2x80x9cMagnetic Tape Head Assemblyxe2x80x9d filed Sep. 29, 1997 by R. Dee et al. and Ser. No. 08/975,645 titled xe2x80x9cMagnetic Tape Head Assembly Having Segmented Headsxe2x80x9d filed Nov. 21, 1997 by R. Dee et al., both of which are incorporated by reference herein. Another design has pairs of read elements and write elements constructed in the same module. At least two modules are joined together to permit read-after-write tape operation in either direction. Designs of this type are described in U.S. Pat. No. 5,264,981 titled xe2x80x9cMultilayered Ferromagnetic Film And Magnetic Head Employing Same,xe2x80x9d U.S. Pat. No. 5,208,714 titled xe2x80x9cMagnetic Hybrid Interleaved Head With Closure Supporting Islands,xe2x80x9d and U.S. Pat. No. 5,142,768 titled xe2x80x9cMethod For Making Magnetic Head With Enhanced Poletip,xe2x80x9d each of which are incorporated by reference herein.
In designs having read and write elements in the same module, alignment errors between paired read and write elements may be compensated by changing the azimuth angle. The azimuth angle is defined as the angle between a line running along the center of the data track and a line through the center of corresponding read and write elements. One problem with this technique in multiple module tape heads is that changing the azimuth angle to improve element alignment within one module may worsen element alignment in another module. Another difficulty is that increasing the azimuth angle introduces a skew distance in the tape direction between write elements and between read elements. The skew distance causes the same point along the length of a data track in each data track across the width of the tape to cross write elements or read elements at a different time. This skew time requires the introduction of skew buffers to ensure proper writing and reading of data. Skew compensation buffers are expensive and require complicated logic.
Alignment problems may be even greater in tape heads constructed with separate read and write modules. Since it is unlikely that a line can be drawn through the center of all elements accessing a given data track, changing the azimuth angle will not correct for alignment problems in tape heads having separate read and write modules.
What is needed is a system and method for highly aligned elements within a magnetic tape head. The tape head should be economical to produce and should be constructed by readily available manufacturing processes.
It is an object of the present invention to provide for improved tape head element alignment.
Another object of the present invention is to provide for decreased skew distances in read-write modules.
Still another object of the present invention is to provide for decreased element alignment errors in multiple module tape heads.
Yet another object of the present invention is to provide a tape head having closely aligned read and write elements that are constructed using readily available manufacturing processes.
A further object of the present invention is to provide a tape head having closely aligned read and write elements that is economical to produce.
In carrying out the above objects and other objects and features of the present invention, a method for manufacturing a thin film tape head having multiple write elements and at least one read element corresponding to each write element is provided. Alignment is achieved by trimming excess material from each write element to align the write element with the at least one corresponding read element. This trimming may be accomplished using a focused ion beam.
A thin film read-write-read tape head is provided. The tape head includes a write module having write elements. Each write element has a top pole and a bottom pole for writing a data track, the data track width defined by the lengths of the top pole and the bottom pole. The tape head also includes one read module on either side of the write module. Each read module has a read element corresponding to each write element for reading the data track. The poles are trimmed to remove excess pole material outside of a desired data track width centered across a line between corresponding read elements in each read module.
A method for manufacturing a thin film tape head includes constructing at least one write module having multiple write elements. Each write element includes top and bottom poles constructed with excess material in a direction defining data track width. The write module is assembled between two read modules. Each read module has a read element corresponding to each write element. Excess material to be removed from the top pole and the bottom pole of each write element is determined such that material remaining forms a write element having a desired track width aligned between the corresponding read elements. The excess material is then trimmed from the top pole and the bottom pole of each write element.
In an embodiment of the present invention, determining the excess material to remove includes measuring the location of the center for each of the two read elements corresponding to a write element. An azimuth line from the first read element center through the second read element center is determined. The intersection of the write element center along the azimuth line is determined. The excess material is that portion of the top pole and the bottom pole outside of a region defining a desired data track width centered on the intersection. The tape head may then be mounted such that the azimuth line is parallel with either tape direction.
A thin film read-write module is also provided. The read-write module includes write elements aligned along a gap line. Each write element has top and bottom poles for writing a data track. The data track width is defined by pole lengths. The module also includes a read element corresponding to each write element for reading the data track. The top and bottom pole lengths are trimmed to remove excess pole material outside of a desired data track width centered across a line through the corresponding read element center and normal to the gap line.
A method of manufacturing a read-write module is provided. The read-write module includes write elements aligned along a gap line and a read module corresponding to each write element. The center of a read element is located. An azimuth line normal to the gap line and through the center of the read element is determined. Excess material from the write element top and bottom poles is trimmed such that a desired data track width is centered on the azimuth line.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.